You don't say what your standard lens is, and I don't know what they fitted to the EOS 500.

For a full frame camera such as yours, a good 24-70 f2.8 zoom is possibly the most useful general purpose lens, although such wide glass is heavy, bulky and pricy. The Canon L variety is very good but horrendously expensive. The Tamron and Sigma versions are more affordable. Add to that a 70-200 f4 and you should be able to cover most eventualities. If your general photography follows a simuilar pattern to mine, the 24-70 would be on the camera most of the time.

You might consider a cheap and cheerful, but optically sound, f1.8 50mm for low light shooting, but a small tripod might be more generally useful.

Thinking this over, for the price of a Canon 24-70L you could buy a nearly new digital Samsung GX10, or Pentax K10D two lens set up, and have enough money left over to pay for half of your fare!